The present invention relates to an electric motor, provided in particular as a windshield-wiper motor in a motor vehicle.
Such an electric motor is described in German Patent No. DE 19727 119. The known electric motor has an armature with an armature shaft that is rotationally mounted by an armature-shaft bearing on each side of armature windings in a housing of the electric motor. The housing can also be a transmission housing or the housing of another device which is driven by the electric motor and is connected with positional accuracy to the electric motor. One of the two armature-shaft bearings is a roller bearing (ball bearing) whose inner ring is pressed for axial fixation onto the armature shaft. An outer ring of the armature-shaft bearing is inserted in a bearing seat in the housing and is axially secured by a spring washer inserted into a groove in the housing. This manner of axially securing the armature-shaft bearing in the housing of the electric motor has the disadvantage that it is costly. Another disadvantage of axially securing the armature-shaft bearing in the bearing seat of the housing in this manner is that it is not possible when the bearing seat is not accessible on the side on which the spring washer is inserted into the groove in the housing. The axial securing of the armature-shaft bearing in the bearing seat of the housing requires an installation opening in the housing.
The housing of the electric motor of the present invention, has a detent or snap-fit connection which retains the armature-shaft bearing axially in the bearing seat with or without play. To assemble, the armature-shaft bearing is introduced axially into the bearing seat until the detent or snap-fit connection engages or snaps into place; the armature-shaft bearing is secured axially in the bearing seat, with or without play, simply by inserting the armature-shaft bearing into the bearing seat without further assembly steps. The armature-shaft bearing is secured axially in the housing of the electric motor quickly, simply and cost-effectively, because the armature-shaft bearing can already be mounted on the armature shaft during the insertion into the bearing seat of the housing, and can be inserted with the armature shaft into the bearing seat of the housing. Another advantage is that the bearing seat does not need to be accessible for inserting the armature-shaft bearing, since the armature-shaft bearing is automatically secured axially in the bearing seat of the housing. In this context, to be understood by a detent connection or snap-fit connection is a connection having a detent or snap element which is pressed elastically to the side when inserting the armature-shaft bearing into the bearing seat, and springs back into its starting position when the armature-shaft bearing has gotten over the detent or snap element, the detent or snap element retaining the armature-shaft bearing axially in the bearing seat by form closure. In the case of a snap-fit connection, when withdrawing the armature-shaft bearing from the bearing seat by sliding the armature-shaft bearing along an inclined plane of the snap element, the snap element is pressed elastically to the side; the snap-fit connection is releasable by withdrawing the armature-shaft bearing from the bearing seat, in that the spring tension of the snap element is overcome. The detent connection is not releasable by the axial withdrawal of the armature-shaft bearing from the bearing seat, since its detent element does not have such an inclined plane.
In a further embodiment of the present invention, the armature-shaft bearing is fixed in position in the bearing seat by tamping (fullering) the housing of the electric motor in the region of the bearing seat. An inwardly projecting collar can be produced on the bearing seat by the tamping, the collar retaining the armature-shaft bearing in the bearing seat by form closure. Another possibility is to work housing material into one or more depressions in the periphery of the armature-shaft bearing by tamping, the armature-shaft bearing thereby being fixed in position in the bearing seat by form closure, as well. The armature-shaft bearing can also be jammed in the bearing seat by tamping; thus, a frictionally-engaged connection can be produced by force locking. Fixing the armature-shaft bearing in position by tamping has the advantage that the bearing seat likewise does not have to be accessible, since the tamping can be carried out from an outer side of the electric-motor housing.
An embodiment of the present invention is provided in particular for a plain (sliding) bearing as an armature-shaft bearing which, unlike a roller bearingxe2x80x94whose inner ring is pressed onto the armature shaft and which consequently is fixed axially on the armature shaft and can be pressed with the armature shaft into the bearing seatxe2x80x94is displacable axially on the armature shaft and therefore cannot be pressed like a roller bearing with the armature shaft into the bearing seat.
The present invention is particularly provided for an armature on whose armature shaft a worm is integrally applied by reforming (non-cutting shaping). The armature-shaft bearing is arranged on the armature shaft between the worm and the armature windings, a commutator usually being disposed between the armature windings and the armature-shaft bearing. If the worm has a larger outside diameter than the armature shaft, the armature-shaft bearing must be mounted on the armature shaft prior to producing the worm, and therefore inserted with the armature shaft into the bearing seat in the housing. In such an electric motor, the armature seat is usually covered by the armature windings, and is therefore not accessible for mounting a securing element fixing the armature-shaft bearing axially in position in the bearing seat.
In a refinement of the present invention the housing has a longitudinal-play stop for the armature shaft which is produced by reforming and which limits the axial play of the armature shaft. The axial play is set by reforming to a designated value which can also be zero. This refinement of the present invention is particularly advantageous when the armature shaft is supported with plain bearings that do not permit an axial fixation of the armature shaft, known from roller bearings, by an arrangement of a locating bearing and a floating bearing or two one-direction thrust bearings.